Currently, various types of image display apparatus become widespread. A projection display method in which the modulated light emitted from the light source is projected onto a screen to display the image exists in such image display methods adopted in the various types of image display apparatus. Conventionally, a lamp light source is used as the light source of the image display apparatus in which the projection display method is adopted. However, the lamp light source has problems such as a short lifetime, a restricted color reproducible region, and low light use efficiency.
In order to solve the problems of the lamp light source, use of a laser light source is recently attempted for the light source of the projection display. In the present invention, the image display apparatus in which the laser light source is used as the light source is referred to as a laser image display device, and similarly the image display screen in which the laser light source is used as the light source is referred to as a laser image display screen. Compared with the lamp light source, the laser light source of the laser image display device has the longer lifetime, and the light use efficiency is easily improved because of strong directional characteristics possessed by the laser beam. The laser beam emitted from the laser light source has excellent monochromaticity, and a color reproducible region can be enlarged to vividly display the image compared with the lamp light source.
FIG. 1 is a schematic diagram of a configuration of a conventional laser image display device. In order to be able to display a color image, the laser image display device 100 includes three-color light sources having a red (R) laser light source 1R, a green (G) laser light source 1G, and a blue (B) laser light source 1B. The red, green, and blue laser beams emitted from the laser light sources 1R, 1G, and 1B are guided to and transmitted through an optical integrator 2. In the laser beam outgoing from the optical integrator 2, a light intensity distribution has a substantially even rectangular section. After the laser beam passes through an illumination optical system 3 (such as a relay lens, a mirror 3a, and a field lens 3b), the laser beam is incident to a spatial light modulation element 4. The spatial light modulation element 4 modulates the laser beam so as to form a two-dimensional image. The modulated red, green, and blue laser beams are multiplexed by a dichroic prism 33 and projected onto a screen 10 through a projection lens 34, and a full-color two-dimensional image is formed on the screen 10.
For years, as to the full-color two-dimensional image displaying with such laser image display device, many proposals are made to enlarge the color reproducible region. For example, Patent Document 1 (JP No. 10-293268 A) proposes a method for enlarging the color reproducible region by using the red laser beam having a wavelength of 625 to 635 nanometers and the blue laser beam having a wavelength of 455 to 465 nanometers as the wavelengths of the laser beams emitted from the laser light sources.
On the other hand, as to the color reproduction with the display apparatus, in order to ensure the broad color reproducible region as much as possible, when one of R (red), G (green), and B (blue) primary colors is displayed, conventionally the primary color is displayed by using a color corresponding to vertices of a polygon (triangle) formed by the color reproducible region possessed by the display apparatus in an xy chromaticity diagram.
Similarly, in the laser image display device, when one of R (red), G (green), and B (blue) primary colors is displayed, it is thought that the broad color reproducible region is effectively utilized by displaying the primary color using the color corresponding to the vertex of the polygon (triangle) formed by the color reproducible region in the xy chromaticity diagram.
Thus, in the laser image display device, the color reproducible region can be enlarged by utilizing characteristics of the laser light source which is of the light source of the laser image display device. However, in the full-color image display with the laser image display device having the enlarged color reproducible region, there are few proposals concerning a method for improving quality of displayed image.
Patent Document 1: JP No. 10-293268 A